System(s), method(s) and device(s) for the prevention of esophageal fistula during catheter ablation

ABSTRACT

The present invention is directed to systems, devices and methods for trans-septally delivering carbon dioxide through a minimally invasive catheter to create a gaseous pocket or emphysema between the posterior wall of the left atrium and the esophagus during cardiac ablation of the left atrium. This pocket of gas expanded tissue serves to thermally insulate and separate the esophagus from the left atrium during ablation to prevent the formation of an atrial-esophageal fistula. The system comprises a control system to precisely deliver the gas to a desired location through a needle-based catheter assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of U.S. ProvisionalApplication No. 62/631,359 filed Feb. 15, 2018.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to systems, methods and devices forpreventing esophageal fistula formation, and more particularly tosystems, methods and devices for preventing esophageal fistula formationafter intra-cardiac catheter ablation of the left atrium.

2. Discussion of the Related Art

Cardiac arrhythmias, and atrial fibrillation, persist as common anddangerous medical ailments, especially in the aging population. Inpatients with normal sinus rhythm, the heart, which is comprised ofatrial, ventricular, and excitatory conduction tissue, is electricallyexcited to beat in a synchronous, patterned fashion. In patients withcardiac arrhythmias, abnormal regions of cardiac tissue do not followthe synchronous beating cycle associated with normally conductive tissueas in patients with normal sinus rhythm. Instead, the abnormal regionsof cardiac tissue aberrantly conduct to adjacent tissue, therebydisrupting the cardiac cycle into an asynchronous cardiac rhythm. Suchabnormal conduction has been previously known to occur at variousregions of the heart, for example, in the region of the sino-atrial (SA)node, along the conduction pathways of the atrioventricular (AV) nodeand the Bundle of His, or in the cardiac muscle tissue forming the wallsof the ventricular and atrial cardiac chambers.

Atrial fibrillation affects millions of Americans. Patients with atrialfibrillation have a significantly increased risk of suffering stroke,heart attack, leg loss, and other adverse events. Intra-cardiac catheterablation has emerged as the dominant therapy for treating atrialfibrillation. By creating full-thickness lines of scar tissue in theleft atrium, the chaotic waves of electrical activity necessary tomaintain atrial fibrillation are isolated, and the patient's heartrhythm converts to a regular organized one. The lines of scar tissuemust be full-thickness, which is to say, must extend from the innerlining of the heart, the endocardium, all the way through the entirethickness of the atrial wall to the outer lining, the epicardium. If thescar tissue is only partial-thickness, the electrical waves can stillpropagate around the scar.

Biosense Webster is a global leader in the field of treating atrialfibrillation. The Biosense Webster CARTO® 3 system allows accuratemapping of the atrium, navigation inside the atrium with an ablationcatheter, and creation of full-thickness lesions. Despite thesophistication of the Biosense Webster system, avoiding occasional postprocedural development of an atrial-esophageal fistula remains achallenge. This complication occurs because of the proximity between theesophagus, the swallowing tube that connects the mouth or moreaccurately, the pharynx to the stomach, and the back wall of the leftatrium.

When creating the pattern of left atrial scar that has been identifiedas most effective in converting atrial fibrillation, it is necessary tocreate a line that runs transversely across the back wall of the leftatrium. During creation of this line, the esophagus may be scarred. Thisis particularly challenging because usually there is no evidence duringthe procedure that suggests the esophagus has been injured. The classicpresentation is that of a patient who returns two weeks after a“successful” ablation with a low-grade fever of unknown origin or asmall stroke. On further investigation, it is revealed that the patienthas developed endocarditis, an infection of the heart and heart lining,resulting from drainage of esophageal contents into the heart, or thatthe patient has had a stroke which resulted from a small bubble of airarising from the esophageal lumen that has passed into the left atrium.Regardless of presentation, the development of an atrial esophagealfistula or abnormal passageway is a potentially serious complication.Patients generally must undergo a major thoracic operation if crisis isto be averted.

Catheter ablation for converting atrial fibrillation to normal organizedrhythm requires the successful creation of full-thickness lines of scartissue in a prescribed pattern throughout the left atrium. One of thelines, by necessity, crosses the back wall where the left atrium and theesophagus are in close proximity. In a significant percentage of cases,the esophagus is inadvertently injured during creation of this burn,which on occasion (0.5 percent to 1.5 percent) results in the delayedformation (approximately two weeks later) of a left atrial-to-esophagealfistula. If the burns do not involve the full thickness of the leftatrium wall, the therapy is unlikely to be successful. Electric currentmay still travel through the partial thickness of living heart muscleand the atrial fibrillation persists. Because of increased awareness ofthis complication, electrophysiologists less aggressively ablate tissueas they cross the back wall, and fewer patients benefit from successfulconversion to regular rhythm as a result. There is consensus amongelectrophysiologists that a solution is needed to allow aggressivetreatment of the left atrium without risk of this potentialcomplication.

Others have proposed solutions. The two main types are: 1) devices thatutilize a shaped balloon, rod, or nitinol structure in an effort to pullthe esophagus away from the back wall of the left atrium so theelectrophysiologist can be more aggressive creating posterior burns; or2) devices passed down the esophagus that measure temperature,impedance, or other metrics to inform the electrophysiologist when it issafe to burn and when it is not, or when the esophagus is heating upduring ablation so the electrophysiologist can stop immediately.

The challenges with the first type include the need for theelectrophysiologist to manipulate the esophagus, something with whichthey typically have little familiarity, and the challenges with movingthe esophagus. The two structures, the esophagus and the left atrium,are immediately adjacent to each other in an air-tight space. As onepulls the esophagus away from the left atrium, the atrium is pulledsomewhat in conjunction with the esophagus. Moreover, there have beenreports of esophageal injury while trying to pull the esophagus byapplying traction to it from within its lumen. These injuries includeoccasional esophageal hematomas, which may require surgical treatment.

The challenges with esophageal temperature monitoring center around itsreactive nature. This monitoring only allows the electrophysiologist todetermine that the esophagus lumen has increased in temperature,indicating that a thermal insult to the esophageal wall has alreadyoccurred. Although this measurement allows the electrophysiologist toimmediately stop burning and in so doing, limit the extent of thethermal exposure, the measurement does nothing to prevent such injuryfrom happening.

Accordingly, there exists a need for a reliable system, method anddevice for preventing esophageal fistula formation during intra-cardiaccatheter ablation of the left atrium.

SUMMARY OF THE INVENTION

The present invention is directed to system(s), method(s) and device(s)wherein sufficient volumes of carbon dioxide gas is injected into thelayer of connective tissue that sits between the esophagus and the backwall of the left atrium to create a protective layer of insulation thatwill prevent thermal injury to the esophagus while intentionallycreating full-thickness burns in the left atrium. The present inventionovercomes a number of the limitations associated with the prior art asbriefly described above.

In accordance with one aspect, the present invention is directed to asystem for the prevention of an esophageal fistula during intra-cardiacablation of the left atrium. The system comprising an injection catheterhaving an elongated body with a proximal end and a distal end, theinjection catheter comprising a Tuohy Borst valve, an outer sheath, ahypo tube having a proximal end and a distal end and slidably positionedwithin the outer sheath, a needle connected to and in fluidcommunication with the distal end of the hypo tube at the distal end ofthe injection catheter, and an anchoring device connected to the outersheath at the distal end of the injection catheter; a gas supplyconfigured to deliver gas to the needle through the hypo tube, the gassupply being connected at the proximal end of the hypo tube; and afeedback control system configured to regulate the pressure and flowrate of the gas from the gas supply to the needle.

Carbon dioxide insufflation, unlike these other approaches, creates aninsulating sleeve around the esophagus, in effect isolating theesophagus from the posterior left atrium wall. The reference “AnatomicRelations Between the Esophagus and Left Atrium and Relevance forAblation of Atrial Fibrillation,” Circulation 2005; 112:1400-1405,describes the heterogeneity with respect to the amount and thickness offibro-fatty tissue interposed between the esophagus and the left atrium.In almost half of the cadavers they dissected, the thickness is lessthan 5 mm. When carbon dioxide is injected into this fibro-fatty layer,the tissue inflates, and becomes “emphysematous,” a term that describessolid tissue infused with gas. The best analogous example from thenon-medical world is from foods, such as cotton candy or marshmallows.Each is made from a small volume of sugar that is increased in volume byinfusing room or ambient air. Sugar has a density of 1.6 g/cm³ andmarshmallow has a density of about 0.4 g/cm³. The volume is increased bya factor of four (4) by infiltrating with air. Similarly, cotton candyhas a density of 0.005 g/cm³. It is over ninety-nine (99) percent air.It is also no coincidence that cotton candy looks like the insulationthat home builders use when building energy efficient homes. Trappedgas, that is, gas that is not free to blow away with a slight breeze ormovement, is an excellent insulator. That explains why Styrofoam®insulates so well (poly-styrene infused with gas), and why fur coats anddown feather jackets are so warm. Trapped gas acts as a superbinsulator.

In accordance with the present invention, the 3 mm to 6 mm layer offibro-fatty tissue that separates the posterior left atrium wall fromthe esophagus will be converted into a thicker layer of gas infusedtissue that will surround the esophagus and provide adequate thermalinsulation, thereby preventing it from being injured. Carbon dioxide isutilized instead of air to leverage carbon dioxide's water solubility.This has no effect on the ability of carbon dioxide to serve as aninsulator as it will behave just like air in this regard, but if carbondioxide is injected directly into the left atrium, there will be noadverse sequelae. Carbon dioxide is so soluble that it goes readily intosolution when pressurized. It makes it highly unlikely to create acarbon dioxide gas embolus, and thereby makes it safe to use inside theleft atrium at dosages less than 3 mL/kg. It is important to note thatdosages of carbon dioxide less than 3 mL/kg that has been introducedinto the cranial circulatory system is tolerated with no neurotoxicity,but the potential to cause embolic stroke in the cranial system doesexist (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4603680/). Because agas is being injected, the needle to be utilized may be small enough,e.g. on the order of a 27-gauge needle, so that the risk of potentialinjury to the left atrium or esophagus is essentially non-existent.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the invention will beapparent from the following, more particular description of preferredembodiments of the invention, as illustrated in the accompanyingdrawings.

FIG. 1 is a block diagram representation of an exemplary system for theprevention of esophageal fistula during intra-cardiac ablation inaccordance with the present invention.

FIG. 2 is a diagrammatic representation of the proximal portion of anexemplary catheter system in accordance with the present invention.

FIG. 3 is a diagrammatic representation of an exemplary Tuohy Borstvalve portion of an injection catheter in accordance with the presentinvention.

FIGS. 4A-4D are diagrammatic representations of the distal portion of afirst exemplary catheter system in accordance with the presentinvention.

FIG. 5 is a diagrammatic representation of the distal portion of asecond exemplary catheter system in accordance with the presentinvention.

FIG. 6 is a graphical representation of flow rate versus needlepenetration depth for various regions of the anatomy in accordance withthe present invention.

FIG. 7 is a graphical representation of voltage versus needlepenetration depth for various regions of the anatomy in accordance withthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to system(s), method(s) and device(s)for preventing or minimizing the formation of an esophageal fistula oresophageal tissue damage due to unintended thermal dispersion duringintra-cardiac ablation of the left atrium. In the present invention,carbon dioxide is injected or infused into the fibro-fatty tissue thatseparates the posterior left atrium wall from the esophagus to expandthe tissue and create an insulation layer therebetween. With the carbondioxide infused tissue insulation layer in place, catheter ablation maybe utilized to create full-thickness scar tissue with minimal risk ofdamaging the esophagus and forming an esophageal fistula. A descriptionof experiments given below demonstrate the feasibility and efficacy ofthe inventive concept.

An eight-animal study was conducted to demonstrate that carbon dioxidecould be safely injected through a catheter inserted up the femoral veinto the right atrium and through the right atrial wall into thepericardium to facilitate obtaining pericardial access. The studydemonstrated that carbon dioxide may be safely injected into biologicaltissue. The study also demonstrated that carbon dioxide offers a numberof advantages over air, including high solubility, low viscosity,radio-translucency and excellent thermal and electrical insulationqualities. More specifically, carbon dioxide which is fifty-four timesmore soluble than nitrogen and twenty-eight times more soluble thanoxygen, is typically reabsorbed in less than two hours and is highlyunlikely to result in gas embolus, even in large quantities, due to itssolubility in water. Carbon dioxide has a low viscosity, allowing it topass through a needle as small as a 33-gauge needle. The puncture fromthis size needle seals almost immediately after removal, even in thepresence of systemic heparin, thereby reducing the likelihood ofcomplications. Carbon dioxide is also visible under X-ray fluoroscopy,thereby allowing for visible confirmation of successful insufflation bycreating an outline of the esophagus under X-ray fluoroscopy. Finally,carbon dioxide is a good electrical and thermal insulator which isexactly what is required to protect the esophagus during intra-cardiaccatheter ablation.

The eight-animal study was followed with two separate acute animalexperiments. In each, the esophagus of a pig was exposed through a leftthoracotomy. Because the esophagus does not run behind the left atriumin pigs, it was possible to directly observe the juxta-esophageal tissueas an indicator of the feasibility of carbon dioxide injection to createa protective barrier layer. A carbon dioxide source was connected to astopcock which allowed a 60-cc syringe connected to a 27-gauge needle tobe filled with pure carbon dioxide. The carbon dioxide was injected intothe soft tissue surrounding the esophagus. The carbon dioxideimmediately dissected through the soft tissue surrounding the esophagusand increased the thickness of the fibro-fatty layer by creating anemphysema (carbon dioxide infused tissue). The carbon dioxide infusedthrough the tissue all the way around the circumference of the esophagusand tracked toward the head and tail as far as the esophagus wasexposed. The thickness of the barrier layer was demonstrated by cuttingtherethrough. The thickness of the gas-infused tissue was visible onX-ray, presenting as a lucent halo around the esophagus. One may alsoappreciate that the esophagus moved away from the spine due to thecircumferential nature of the carbon dioxide emphysema. Essentially, thecarbon dioxide emphysema isolates the esophagus from all otheranatomical structures.

Upon completion of the pig studies, two human cadaver studies wereconducted to demonstrate the feasibility of forming an insulation layeraround the esophagus by creating an emphysema. In both cadavers, asimple investigation was conducted by injecting 120 cc (two complete 60cc syringes) of carbon dioxide through the back wall of the left atrium.This was also done under direct vision, as the heart in each of thecadavers had been dissected. This study was an endeavor to demonstratethe feasibility of the concept of forming an insulation layer bycreating an emphysema or separation. After cutting through the posteriorleft atrium wall, it was observed that emphysematous tissue between theleft atrium and the esophagus formed as it did in the animal studiesutilizing carbon dioxide.

The animal experiments were then repeated with additional steps. Anesophageal temperature probe was utilized to monitor tissue temperaturewhile intentionally creating lesions on the outer surface of theesophagus using an ablation catheter. Ablation of the esophageal wallwas performed both with carbon dioxide insufflation and without carbondioxide insufflation, to learn of the effects carbon dioxide has on theconduction of thermal energy.

In these evaluations, the esophagus was exposed through a large leftthoracotomy. A multi-pole temperature probe was placed through the pig'smouth and down the esophagus under X-ray guidance. The ablation catheterwas applied directly to the outer surface of the esophagus and theablation electrode was aligned with one of the twelve (12) poles of thetemperature sensor by X-ray. The ablation catheter was then energized.The measured temperature began to climb almost immediately, from abaseline temperature of 36.6 degrees C., reaching the critical 0.2degrees C. increase in less than five (5) seconds. With continued energyapplication, the temperature rose to 40 degrees C. after thirty (30)seconds. The experiment was then repeated under the same conditions,with the only difference being carbon dioxide insufflation was added tothe protocol as is explained in greater detail subsequently.

Prior to infusing carbon dioxide to test thermal insulation of theesophagus during ablation, an investigation into how long carbon dioxidewould remain in place after injection into the peri-esophageal space wasperformed. After injecting 120 cc of carbon dioxide into theperi-esophageal fibro-fatty tissue, the tissue would instantly inflatewith carbon dioxide, becoming considerably thicker. Yet, the tissuewould gradually return to baseline geometry after approximately five (5)minutes. From this simple test it may be reasonably inferred thatcontinuous insufflation with carbon dioxide would be preferable toinsuring the insulating layer remained in place when needed during theablation procedure.

Based on this observation, a 27-gauge needle attached to a longintravenous extension tube was attached directly to the regulator of asmall tank of pressurized carbon dioxide. When the needle was insertedinto the fibro-fatty tissue around the esophagus, it immediatelyinflated, as had been previously observed. But the cavity remainedinflated until the supply of carbon dioxide was stopped. The rate ofcarbon dioxide delivery was arbitrarily titrated to be as low aspossible with the regulator at hand.

When this experiment was repeated with an ablation catheter and atemperature probe (once again aligning the electrode with thetemperature sensor under X-ray) and performing the ablation burn at thesame power settings, the temperature readings were significantlydifferent from those observed prior to infusion of carbon dioxide. Afterthirty (30) seconds of continuous burning, the temperature rose only 0.1degrees C., from 36.6 degrees C. to 36.7 degrees C., in contrast to the3.4 degrees C. observed when there was no carbon dioxide present;namely, 36.6 degrees to 40.0 degrees C. Accordingly, carbon dioxideinjected into the fatty tissue surrounding the esophagus providedthermal insulation to the esophagus during such a procedure.

Dissection of the peri-esophageal tissue after only 120 cc of carbondioxide injection or infusion reveals an 8 mm sheath or layer ofemphysematous tissue that circumferentially surrounded the esophagus.This tissue is gas infused and conducts radio frequency energy and heatpoorly. This 8 mm layer should push the posterior left atrium wall andthe esophagus away from each other, thereby allowing aggressive burns tobe created across the posterior left atrium wall without fear ofesophageal injury.

A system for performing this procedure should preferably be simple forthe electrophysiologist to utilize and not interfere with the underlyingintra-cardiac catheter ablation procedure. The system should preferablyremain in position during the ablation and cause no injury to the leftatrium, the esophagus or any biological tissue. The system may alsocounter the effects of systemic carbon dioxide absorption by utilizing afeedback controller to deliver additional carbon dioxide as needed tomaintain the required tissue separation. The system may include atemperature probe. Initially, doctors may place a temperature probe inthe esophagus to ensure that the carbon dioxide infused tissue doescreate a thermal barrier. Once enough evidence exists that proves thatthe esophagus is thermally insulated, the temperature probe may not beneeded. The system may also be utilized just once at the onset of theintra-cardiac catheter ablation procedure to achieve the desiredseparation between the esophagus and the left atrium and thensubsequently removed to allow for the remainder of the ablationprocedure, provided the effects of carbon dioxide absorption arenegligible.

A system in accordance with the present invention preferably comprises areversibly deployable needle that advances a short distance from the endof a catheter and locks in that position, but that is in fixed geometricrelationship to a sensor that allows its position to be identified on amapping device such as CARTO® 3, and that has a mechanism for fixing thecatheter in place, to prevent it from falling out during ablation. Thesystem also comprises a valve, button, knob or any suitable device thatconnects the catheter to a small pressurized canister of carbon dioxidewith a built-in regulator that: 1) controls the rate and volume ofcarbon dioxide that can be delivered over the course of the procedure;and 2) for safety, makes it impossible to accidentally hook the deviceto a gas other than carbon dioxide. The system should also preferablycomprise a custom sheath that allows the catheter to be inserted acrossthe atrial septum and locked into position on the posterior left atriumwall, while providing a second lumen for the ablation catheter to beinserted into the left atrium for creation of the burns. Alternativeexemplary embodiments are also contemplated as described in greaterdetail subsequently.

More specifically, an injection catheter for administering carbondioxide through the left atrium wall as part of the above-describedsystem preferably has certain attributes. The injection catheter shouldfit through a standard 8.5 French trans-septal sheath and have anintegrated stop cock and syringe to allow sterile carbon dioxide to bedrawn and delivered. In an alternative exemplary embodiment, theinjection catheter may comprise an integral sterile carbon dioxidecanister to decrease the setup time and make it easier to utilize. Theinjection catheter should preferably have the right handlingcharacteristics and column strength to allow the needle to be advancedprecisely at the desired point. In one exemplary embodiment, the needleassembly should preferably comprise a 27-gauge needle that only extendsto the epicardium to ensure accurate carbon dioxide delivery. In analternative exemplary embodiment, the 27-gauge needle may extend beyondthe epicardium.

In an alternative exemplary embodiment, a catheter with balloons and adeployable needle that is placed through the pharynx and into theesophagus which allows injection of carbon dioxide into these samefibro-fatty tissues through the esophageal wall, in other words “insideout” from the esophageal lumen outward may be utilized. In thisalternate exemplary embodiment, the catheter would be similar to thecatheter described above.

Referring now to FIG. 1, there is illustrated an exemplary embodiment ofa system 100 for the prevention of esophageal fistula duringintra-cardiac catheter ablation in accordance with the presentinvention. The system 100 is configured to trans-septally deliver carbondioxide through a minimally invasive catheter to create a gaseous pocketbetween the posterior wall of the left atrium and the esophagus. Thispocket serves to thermally isolate and separate the esophagus from theleft atrium during ablation to prevent the formation of anatrial-esophageal fistula. It is important to note that the system 100may be implemented utilizing a combination of discrete components, as aunitary, integrated system and/or a combination thereof.

The system 100 is configured as a closed-loop feedback control systemand is illustrated in block diagram format for ease of explanation.Carbon dioxide, purified for use in biological applications, is suppliedfrom a pressurized canister 102 and routed through a conduit 101 to apressure regulator 104. As set forth above, special connectors may beutilized to prevent gas supplies other than carbon dioxide from beingutilized. Although illustrated as a single discrete carbon dioxidecanister, the gas may be supplied from any suitable source, for example,a central supply. In addition, the pressure regulator 104 may beconnected directly to the pressurized canister 102. The pressureregulator 104 is electronically adjustable and is utilized to set andmaintain the pressure at which the carbon dioxide is delivered. Theoperation of the pressure regulator 104 is the same as a pressureregulator on a SCUBA tank or home compressor. A pressure regulatorsimply maintains the pressure of the gas to be released at a set valuefor downstream use. The pressure regulator 104 is connected to asolenoid-controlled valve 106 through conduit 103. Thesolenoid-controlled valve 106 is utilized to control the flow rate ofthe carbon dioxide from the canister 102 or other supply. Thesolenoid-controlled valve 106 is connected to a flowmeter 108 viaconduit 105. The flowmeter 108 measures the flow rate of the carbondioxide exiting the solenoid-controlled valve 106 to ensure that it isat the desired flow rate for use in the procedure. The flowmeter 108 isconnected to an injection catheter 110 through conduit 107. Theinjection catheter 110, which comprises a needle assembly described ingreater detail subsequently, is utilized to precisely deliver the carbondioxide to the desired location within the body as described herein. Theconduits 101, 103, 105 and 107 may comprise any suitable material thatdoes not react with carbon dioxide, for example, metallic materials suchas stainless steel and polymeric materials such as polysiloxanes.

The system 100 also comprises a microprocessor or microcontroller 112.The microprocessor or microcontroller 112 is powered by a power supply114. The power supply 114 may comprise a battery, either a primarybattery or a secondary battery, and/or circuitry for converting powersupplied from another source, for example, house power, into a voltageand current level suitable for the microprocessor 112 and othercomponents of the system 100. The microprocessor 112 is programmed tooutput control signals to the flowmeter 108 and the catheter 110 basedupon feedback signals from each as well as preprogrammed controlparameters. The microprocessor 112 also outputs control signals to thepressure regulator 104 to adjust the pressure of the gas as required,and to a user control 114. The user control 114 is configured to allowthe user of the system 100, for example, a physician orelectrophysiologist, to set the parameters of operation via itsconnection to the solenoid-controlled valve 106 and operates as part ofthe feed-forward path of the control loop. The microprocessor 112,through its feedback control process automatically adjusts and maintainsthe operation of the system 100 in accordance with the user's settings.The microprocessor 112 may comprise any suitable processor andassociated software and memory to implement the operation of the system100.

It is important to note that all electronics and electrical connectionsare protected in a manner suitable for use in an operating or proceduretheater. These precautions are necessary to prevent any interactionbetween an oxygen source and an electrical spark. In addition, allcomponents are preferably manufactured for medical grade usage.

Referring now to FIG. 2, there is illustrated a diagrammaticrepresentation of the proximal region of an exemplary catheter that maybe utilized for interventional procedures in accordance with the presentinvention. The exemplary catheter comprises an elongate body having aproximal end and a distal end. The exemplary catheter 200 comprises afemale luer lock connector 202 connected to a Tuohy Borst valve 204 viahypo tube 206 at the proximal valve end 208 of the Tuohy Borst valve204. The carbon dioxide supply or pressurized canister 102 illustratedin FIG. 1 is connected to the injection catheter 200 via this connectionpoint. As set forth above, unique connectors may be utilized to preventconnection to a different gas supply. In addition, this connection point202 may be utilized to connect any suitable means for flushing thesystem. The Tuohy Borst valve 204 also comprises a Y-connection 210. TheY-connection 210 may be utilized to introduce fluids for any number ofpurposes, including the delivery of contrast agents for fluoroscopicvisualization. A proximal shaft 212 is connected on one end to a luerconnector 214 of the Tuohy Borst valve 204 via outer shaft luer hub 216and on the other end to a distal shaft, not illustrated. The Tuohy Borstvalve 204, the luer connector 214 and the outer shaft hub 216 arerotationally fixed together to work as a unitary structure. With thisconfiguration, rotation of the Tuohy Borst valve 204 facilitatestransmission of torque down the catheter shaft to a fixation coil, asdescribed in detail subsequently, to engage and advance the fixationcoil into the heart wall during a procedure. The distal end or region ofthe exemplary catheter 200 is continuous with the proximal end or regiondescribed herein; however, for ease of explanation as it relates to thepresent invention, the description and drawings are given independently.This basic catheter structure may be utilized for any number ofinterventional procedures, including the introduction and use of aninjection catheter for the delivery of carbon dioxide. A detaileddescription of the Tuohy Borst valve and the proximal portion of theinjection catheter, and the needle assembly or distal portion of theinjection catheter of the present invention, as stated above, is givensubsequently.

FIG. 3 is a diagrammatic representation of a Tuohy Borst valve 300 inaccordance with the present invention. The Tuohy Borst valve 300 isessentially the proximal region of the injection catheter in accordancewith the present invention. The Tuohy Borst valve 300 comprises aproximal valve 302 with screw lock 304. The proximal valve 302 isthreaded to open and close the valve. The screw lock 304 of the proximalvalve 302 may be turned clockwise to form a liquid tight seal around anyinstrumentation, for example, a hypo tube, introduced therethrough toprovide a pneumostatic and hemostatic seal. The Tuohy Borst valve 300also comprises a threaded luer connector 306 which connects the TuohyBorst valve 300 to the shaft luer hub 216, illustrated in FIG. 2, of thecatheter as described briefly above and in greater detail subsequently.

A deformable O-ring 308 is positioned within the proximal valve 302 suchthat a hypo tube 310 portion of the injection catheter of the presentinvention passes therethrough. It is through this hypo tube 310 andultimately a needle attached thereto that the carbon dioxide isintroduced into the desired tissue. Referring back to FIG. 1, the hypotube 310 is part of the catheter block 110. As the screw lock 304 of theproximal valve 302 is tightened (clockwise for right-handed threads),the O-ring 308 is compressed which decreases its inside diameter. Thisaction creates a compressive friction lock on the hypo tube 310 of theinjection catheter, which may be utilized to lock the needle in placeonce the desired tissue depth is achieved. A second O-ring 312 ispositioned within the threaded luer connector 306 to create acompressive seal for connection to the shaft luer hub 216, illustratedin FIG. 2. The hypo tube 310 of the present invention comprises a stopmechanism 413. The stop mechanism 314 is a structure mounted around thehypo tube 310 in the region between the O-rings 308 and 312 of the TuohyBorst valve 300. The diameter or size of the stop mechanism 314 issufficient to prevent the hypo tube 310 from passing through eithernon-compressed O-ring 308, 312 to prevent accidental over-deployment ofthe needle into the target tissue as well as unintentionalover-retraction of the injection catheter from the introducer ortrans-septal sheath as described in greater detail herein. The hypo tube310 may comprise any suitable biocompatible material, including any hypotube materials currently in use in catheters. The stop mechanism 314 mayalso comprise any suitable biocompatible material. In the exemplaryembodiment, the stop mechanism 314 comprises a polymeric material and isbonded to the hypo tube 310 utilizing any suitable means includingwelding and adhesives.

FIGS. 4A-4D are diagrammatic representations of the distal portion of anexemplary injection catheter in accordance with the present invention.FIG. 4A is a sectional or cutaway view of the distal region of an outersheath 400 of the injection catheter. The outer sheath 400 comprises atubular structure 402 in which an inner sheath 408 is coaxiallypositioned. Attached to the distal end of the outer sheath 400 is afixation coil 404. The fixation coil 404 comprises a corkscrewconfiguration that functions as a reversible anchoring system to securethe injection catheter in place during carbon dioxide insufflation. Thefixation coil 404 is affixed to the outer surface of the distal end ofthe tubular structure 402 such that a first portion thereof is sealed tothe tubular structure 402 and a second portion thereof extends past theend of tubular structure for anchoring in the myocardium. To ensure thatthe fixation coil 404 and the tubular structure 402 move and operate asa unitary structure, the fixation coil 404 is permanently bonded to thetubular structure 402 by any suitable means. In one exemplaryembodiment, a UV curable adhesive is utilized. The tip of the fixationcoil 404 comprises a sharp point 406, illustrated in FIG. 4D, to easilypierce the cardiac tissue. The tubular structure 402 may comprise anysuitably rigid, biocompatible material that may be navigated through atortuous vasculature. Standard catheter materials may be utilized. Thefixation coil 404 may comprise and suitable rigid biocompatible materialthat can be twisted into cardiac tissue and anchor therein. Metallicmaterial, for example, stainless steel, or polymeric materials may beutilized. In the exemplary embodiment, the fixation coil comprisesstainless steel. The most distal end of the outer sheath 400 alsofeatures a radiopaque marker or band 401 for fluoroscopic visualization.The radiopaque marker 401 may be formed from any suitable material, forexample, tantalum and bonded to the outer sheath 400 utilizing anysuitable means. The radiopaque marker 401 is positioned on the outersurface of the outer sheath 400 and bonded within the inside diameter ofthe fixation coil 404.

In operation and prior to needle 410, illustrated in FIG. 4B,deployment, the injection catheter is navigated into a positionproximate the left atrium such that the fixation coil 404 may be screwedinto the myocardium of the left atrium in order to maintain catheterposition during carbon dioxide insufflation. Essentially, the fixationcoil 404 reversibly anchors the outer sheath 400 to the patient's heartby a simple twisting motion of the injection catheter. As set forthabove, twisting or rotation of the Tuohy Borst valve 204, FIG. 2, by thephysician facilitates transmission of torque through the outer sheath400.

FIG. 4B is a sectional or cutaway view of the distal region of the innersheath 408. The inner sheath 408 comprises a needle 410 that may beadvanced through the posterior wall of the left atrium into thejuxta-esophageal space or fibro-fatty tissue to deliver a controlleddose of carbon dioxide during an intra-cardiac catheter ablationprocedure and then removed. The outer sheath 400 prevents the needle 410from contacting the surrounding vasculature during navigation of theinjection catheter to the target insufflation site. The needle 410 maybe retracted back into the outer sheath 400 upon completion of theprocedure. The needle 410, which may comprise any suitable material andbe sized as set forth herein is connected to the hypo tube 310,illustrated in FIG. 3, via a plastic extrusion 412. In the exemplaryembodiment, the needle 410 comprises surgical steel, may comprise anyother suitable metallic materials, including nitinol and highlyradiopaque materials in alternate embodiments. The connection of theneedle 410 to the plastic extrusion 412 and the connection of theplastic extrusion 412 to the hypo tube 310 may be made by any suitablemeans such that an unobstructed flow of carbon dioxide may be achievedwhile allowing the three components to act as a unitary structure. Inoperation, the needle 410 is advanced and retracted by movement of thehypo tube 310 within the outer sheath 400 which is anchored in themyocardium. The needle 410 and the plastic extrusion 412 are coaxiallypositioned within the lumen of the braided shaft forming the innersheath 408 inside of a centering element 414. The needle 410 is alsoslidably sealed to the tip of the inner sheath 408. The centeringelement 414 and the seal 416 may be made of any suitable biocompatiblematerial.

FIG. 4C illustrates the assembled injection catheter distal portion withthe inner sheath positioned within the outer sheath 400 and the needle410 extending therefrom. FIG. 4D illustrates a sectional or cutaway viewof the assembled injection catheter distal portion. As explained herein,the injection catheter is navigated through the vasculature and intoposition proximate the left atrial myocardium. The injection catheter isanchored into position utilizing the fixation coil 404. When properlyanchored, the needle 410 is advanced via the hypo tube 310 at theproximal end until the desired tissue depth is reached. Carbon dioxideis then injected into the fibro-fatty tissue that separates theposterior left atrium wall from the esophagus via the exemplary systemillustrated in FIG. 1 until the ablation procedure is completed. Uponcompletion, the fixation coil 404 is removed by twisting the outersheath 400 in the opposite direction for insertion, and the injectioncatheter may be removed. The injection catheter does not in any wayinterfere with the left atrium ablation procedure. In addition, it isimportant to note that the injection catheter of the present inventionmay be introduced via the same introducer or trans-septal sheath as theablation catheter or a completely different one.

Although the distal portion and the proximal portion of the injectioncatheter is shown in different illustrations for ease of explanation,the two portions form a continuous structure with inner and outersheaths.

In an alternate exemplary embodiment, the needle may be fixed in placewith the fixation coil. Wherein with the exemplary embodiment describedabove the needle moves independently of the fixation coil by means ofthe longitudinal movement of the hypo tube, in this alternate exemplaryembodiment, the needle remains fixed relative to the coil. In otherwords, as the fixation coil is twisted into and out of the cardiactissue, the needle advances or retracts accordingly. FIG. 5 illustratesthis alternate exemplary embodiment. As illustrated, the needle 502 ispositioned within the fixation coil 504 and both are attached to the endof an outer sheath 500 with the needle 502 in fluid communication asdescribed above.

As set forth above, the needle-tipped catheter or injection catheter isadvanced through the posterior wall of the left atrium into thefibro-fatty tissue or juxta-esophageal space to deliver a controlleddose of carbon dioxide to expand the tissue and create an insulationlayer during an ablation procedure. In the preferred embodiment, thedelivery of carbon dioxide is continuous during ablation rather thanthrough discrete delivery so as to safely maintain tissue expansion.Upon completion of the procedure, the needle may be retracted into theouter sheath of the catheter. In order to precisely deliver the carbondioxide, the system may employ one or more methodologies to determinethe deployment depth of the needle without the need for direct visualconfirmation. It is important to note that visual confirmation would bea viable alternative but involve additional complexities.

In one exemplary method, the flow rate of the carbon dioxide exiting theneedle may be monitored to determine the resistance to flow. The leftatrium space, the myocardial tissue and the fibro-fatty tissue all havedifferent resistivity to gas flow. Accordingly, the physician may simplydetermine in which tissue layer the needle tip resides by referencing atissue layer flow rate characterization chart. In an alternativeembodiment, the microprocessor 112 (FIG. 1) may be programmed with theflow resistivity of the various tissues or media in the body andreceiving feedback from the flowmeter 108 as to the flow rate exitingfrom the needle, automatically generate an alert via some suitablesignal to be displayed or an audible signal that indicates that theproper location for the needle has been achieved. The flowmeter may beutilized to measure the flow resistance at the needle tip and providefeedback directly to the physician or through the microprocessor 112rather than flowmeter 108.

FIG. 6 is a graphical representation of the relative flow rates ofcarbon dioxide in the different regions/tissues. The vertical axisrepresents volumetric flow rate and the horizontal axis representsneedle penetration depth in mm. In the first region 602 which representsthe intra-atrial space, the flow rate of carbon dioxide is high relativeto the other regions as one may expect. In the second region 604 whichrepresents the heart wall, the flow rate of carbon dioxide issignificantly lower that the first region 602 given the density of thecardiac tissue. In the third region 606 representing the periesophagealtissue, the flow rate of carbon dioxide is higher than in the heart walldue to lower tissue density but lower than in the intra-atrial space. Bymeasuring flow rate as the needle progresses, one may determine needlelocation.

In another exemplary method, the electrical activity of the tissue inwhich the needle is positioned may be monitored. The myocardium has adistinctly different electrical activity profile than the left atriumspace and the surrounding tissue. By monitoring this activity with theneedle tip, the physician can determine the point at which the needlehas contacted and subsequently passed through the myocardium and enteredinto the fibro-fatty tissue. In this exemplary embodiment, the needlemay be configured to provide feedback to a stand-alone sensing circuitor one that is part of the microprocessor. The sensing circuit may beconfigured to measure the electrical activity, for example,voltage/potential and/or resistance/impedance. As in the previouslydescribed embodiment, this information may be routed through themicroprocessor 112 which will automatically make the determination or toany suitable device for altering the physician.

FIG. 7 is a graphical representation of voltage, or potential, verticalaxis, versus needle penetration depth, horizontal axis. As illustrated,in the first region 702 corresponding to the intra-atrial space, thevoltage sensed by the needle is steady-state and low. In the secondregion 704 corresponding to the heart wall, the electrical activity isnot steady-state and at a higher potential than the first region. In thethird region 706 corresponding to the periesophageal tissue, theelectrical activity is once again steady-state and of lower potentialthan the cardiac tissue of the heart wall.

In both exemplary embodiments, real-time monitoring of needle locationis achieved without the need for direct visualization.

Although shown and described in what is believed to be the mostpractical and preferred embodiments, it is apparent that departures fromspecific designs and methods described and shown will suggest themselvesto those skilled in the art and may be used without departing from thespirit and scope of the invention. The present invention is notrestricted to the particular constructions described and illustrated butshould be constructed to cohere with all modifications that may fallwithin the scope of the appended claims.

1-17. (canceled)
 18. A method for preventing an esophageal fistuladuring intra-cardiac ablation of the left atrium, the method comprisingthe steps of: delivering an injection catheter to a region proximate theposterior left atrium wall; anchoring the injection catheter to thecardiac tissue; advancing a needle of the injection catheter into thefibro-fatty tissue that separates the posterior left atrium wall fromthe esophagus; delivering a dose of gas at a controlled rate through theneedle into the fibro-fatty tissue to create a thicker, gas infusedinsulation layer; and removing the injection catheter when the dose isdelivered. 19-20. (canceled)